MPB64 is a Mycobacterial protein which is produced by Mycobacterium bovis BCG and secreted outside of bacteria cells. Also, MPT64 is known as one of the Mycobacterial proteins that are specifically produced by Mycobacterium tuberculosis and secreted outside of bacteria cells. It is known that MPT64 is the same substance as MPB64. This means that an antibody to MPB64 is also an antibody to MPT64.
Therefore, infection with Mycobacterium tuberculosis complex can be diagnosed by culturing pathogenically harmless Mycobacterium bovis BCG, extracting and purifying MPB64 produced in the culture, obtaining an anti-MPB64 antibody using the MPB64 as an antigen, and detecting MPT64 in a sample by antigen-antibody reaction (immune reaction) using this antibody.
A method for detecting Mycobacterium tuberculosis by immunological method using an antibody to MPB64 (hereinafter, abbreviated as “anti-MPB64 antibody”) is already known (refer to Patent Document 1). In addition, an assay utilizing immunochromatography is also already known as the immunological method (refer to Patent Document 2).
However, these known methods require Mycobacterium tuberculosis complex in a sample to grow by culturing to secrete MPT64 before it is subjected to immunoassay, and the culturing takes about a week.
In addition, even though the conventional immunochromatographic methods have no reactivity with most of non-tuberculous Mycobacteria (NTB) but have a very strong reactivity with Mycobacterium tuberculosis complex, it has been reported that they still show cross reactivity with two strains of non-tuberculous Mycobacteria, i.e., Mycobacterium marinum and Mycobacterium flavescens (Non-Patent Document 1).    Patent Document 1: Japanese Patent Laid-open No. H07-110332    Patent Document 2: Japanese Patent Laid-open No. H11-108931    Non-Patent Document 1: ABE C. et al., “Simple and Rapid Identification of the Mycobacterium tuberculosis Complex by Immunochromatographic Assay Using Anti-MPB64 Monoclonal Antibodies”, Journal of Clinical Microbiology, November 1999, p. 3693-3697